Cannot read properties of undefined

Hi everyone, you might faced this issue while working with Javascript.

Most relatable! I faced this issue many times, how can we handle this?

• First of all, Javascript is not strongly typed language, so it get tricky to handle stuff like this. But, you can use optional chaining operator ?. to handle this scenarios
• Let’s take a example where you need to access value from API response

const response = await fetch("https://jsonplaceholder.typicode.com/posts/1");
const data = await response.json();

// This is the idle value of data
{
  "userId": 1,
  "id": 1,
  "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
  "body": "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto"
}

// Now, let's say you want to access title property from data
console.log("title: ", data.title); // title: sunt aut facere repellat provident occaecati excepturi optio reprehenderit

// But, what if data is undefined or null 🤔
// Assume scenario where API response is null
console.log(data.title); // Uncaught TypeError: Cannot read properties of undefined (reading 'title')

// To handle this, you can use optional chaining operator
// If the data is undefined or null, we will get undefined as output
console.log("title: ", data?.title); // title: undefined

Nice👌

There’re few more operators which can help you with value checking

• Ternary Operator (?:): This operator is simplified version of if else statement, here is an example:

const person = {
  name: "John Doe",
  age: 25,
};

const name = person?.name ? person.name : "stranger";

• Nullish Coalescing Operator (??): This operator is used to check if the value is null or undefined, here is an example:

const person = null;

// If person is null or undefined, name will be "stranger"
const name = person?.name ?? "stranger";

• Tip: Use Typescript because it provides data-types for variables, which can help you to avoid such issues

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